STAT3 and triple-negative breast carcinoma: In MDA-MB-468 cells, a triple-negative breast cancer cell line characterized by constitutive STAT3 phosphorylation, pyrimethamine did not significantly reduce total STAT3 tyrosine phosphorylation (phosphorylated STAT3 [pSTAT3]; Fig. 1A) and only led to a slight reduction in nuclear pSTAT3 and total STAT3 (Fig. 1B).